Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

From: Russell King
Date: Tue Aug 21 2007 - 05:13:44 EST


On Mon, Aug 20, 2007 at 05:05:18PM -0700, Paul E. McKenney wrote:
> On Tue, Aug 21, 2007 at 01:02:01AM +0200, Segher Boessenkool wrote:
> > >>And no, RMW on MMIO isn't "problematic" at all, either.
> > >>
> > >>An RMW op is a read op, a modify op, and a write op, all rolled
> > >>into one opcode. But three actual operations.
> > >
> > >Maybe for some CPUs, but not all. ARM for instance can't use the
> > >load exclusive and store exclusive instructions to MMIO space.
> >
> > Sure, your CPU doesn't have RMW instructions -- how to emulate
> > those if you don't have them is a totally different thing.
>
> I thought that ARM's load exclusive and store exclusive instructions
> were its equivalent of LL and SC, which RISC machines typically use to
> build atomic sequences of instructions -- and which normally cannot be
> applied to MMIO space.

Absolutely correct.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/